Molecular structure of ZnPc (left) and average PDOS of a single atom (right). Pyrrole carbon and benzene carbon are marked as CP (green circle) and CB (red circle). Two coordinated and three coordinated nitrogen atoms are marked as N2c (blue dashed circle) and N3c (blue solid circle).
Core level spectra of C1s (a) and N1s (b) from ZnPc on TiO2. Curve fitting is done for C1s (c) and N1s (d) on selected coverages. PI and BI represent the pyrrole carbon and benzene carbon of interfacial molecules; PB and BB stand for the counterparts on bulk-like molecules. The energy shift is marked by dotted lines. In C1s (c), the shift between PI and PB is about 1.5 eV, while that of BI and BB is 0.8 eV. In N1s, the shift between interfacial molecules and bulk like molecule is around 1.7 eV.
Overview of valence band spectra (left), Zn3d spectra (middle) and HOMO region (right) at different coverages.
N K-edge NEXAFS spectra at different coverages under p polarization (a) and s polarization (b). A and A′ denote the N1s → LUMO transitions of bulk-like molecules and interfacial molecules, respectively. Transition B and C of the bulk like molecule and transition D of the interfacial state molecule represent the ones from N1s to higher empty π* orbitals. (c): the schematic of the molecular orientation ZnPc adsorbed on TiO2(110). Ti is marked in grey circle; O is in red dot; blue ellipse represents the cross-section of ZnPc. The molecule is aligned along  direction which is perpendicular to the paper in the first layer. Horizontal orientation is [10-1] direction and vertical orientation is  direction. The interfacial molecules layer is estimated tilted on the surface at 30°; the thicker layer is packing at 33° under a free azimuthal assumption. In between, there are transition layers, which we cannot determine the angle.
C K-edge NEXAFS spectra from 0.9 ML (top) and 3.8 ML (bottom). Spectra collected under p and s polarization are plotted with black filled dotted line and red open dotted line. A and A1 are transitions from CB and CP to LUMO for the bulk like molecule, while A2 and A3 are attributed to the C1s transitions to LUMO for interfacial molecules. Transition B and C stem from the excitation from C1s to higher empty π* orbitals.
The alignment of PES and NEXAFS for interfacial molecules (left) and bulk-like molecules (right). Single arrow represents the NEXAFS transition. Double arrow marks the core level differences. π* is the lowest excited state for both case, the value is determined by subtracting the excitation energy (hυ) in NEXAFS from the core level EB. For CB1s, the PES binding energy difference matches the photon energy difference in NEXAFS. For N1s, N1s(i) is the initial state while N1s(f) represents the contribution from the additional final state screening in PES. In NEXAFS, the external final screening is not influential and thus mainly the initial state is probed.
Curve fitting parameters in Figure 2.
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